A model of the epidemic dynamics of heartwater within a cattle production unit was presented by
Yonow et al. (1998). Here, the model is expanded to a region consisting of several farms to study the
effect of environmental variability on control strategies. We have shown that:
• In a region, where the environment of each farm is modelled with constant epidemiologic parameter
values, while the between-farm parameter values differ, regional variation in the removal rate
of infected cattle increases the average fraction of infected cattle across the region , while regional
variation in the transmission rate of infection from ticks to cattle decreases the average fraction of
infected cattle, thereby requiring control measures that keep the removal rate uniform and the
transmission rate variable.
• In a region, where in addition to regional variation between farms, the epidemiologic parameters
of each farm are time-variant, then temporal variation in both the transmission rate and removal
rate increases the average fraction of infected cattle across the region, thereby requiring control
measures that keep both parameters uniform.
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